G. M. Arifuzzaman Khan, Md. Ahsanul Haque, and Md. Shamsul Alam

Contents

10.1 Introduction…………………………………………………………………………………………………… 158

10.2 Functionalization of Okra Bast Fibre……………………………………………………………………… 160

10.3 Okra Bast Fibre-Reinforced Phenol Formaldehyde Resin Composites………………………………. 162

10.3.1 Thermosetting Phenol Formaldehyde Resin…………………………………………………. 162

10.3.2 Fabrication Techniques…………………………………………………………………………. 164

10.3.3 Mechanical Properties…………………………………………………………………………… 166

10.3.4 Thermal Degradation……………………………………………………………………………. 169

10.3.5 Biodegradation…………………………………………………………………………………… 171

10.4 Conclusion……………………………………………………………………………………………………. 172

References……………………………………………………………………………………………………………. 172

Abstract Bast fibres are mainly composed of lignocellulosic materials. It is extracted from the outer cell layers of the stems of different plants species. In ancient times, bast fibres were used for making various products like rope, bags, mats and coarse textile materials to mitigate daily demands. However, such trendy usages of bast fibres were decreased behind the invention of cheap synthetic fibre. Although synthetic fibres have good strength and longibility, they are causing serious environ­mental pollution for their nonbiodegradable nature. To achieve the ‘sustainable development’, the usages of bast fibres are explored again. Diversified use of bast fibres as reinforcements of polymer matrix composites becomes popular due to its satisfactory engineering properties. The plant kingdom has a vast source of bast fibres. Few of them are utilized for reinforcing polymer composites and many spe­cies remain unexplored. Okra (Abelmoschus esculentus) bast fibre has no commer­cial value currently. It is considered as agricultural waste product after collecting

G. M.A. Khan (*) • Md. A. Haque • Md. S. Alam

Department of Applied Chemistry and Chemical Technology, Islamic University, Kushtia 7003, Bangladesh e-mail: arif@acct. iu. ac. bd

K. R. Hakeem et al. (eds.), Biomass and Bioenergy: Processing and Properties,

DOI 10.1007/978-3-319-07641-6_10, © Springer International Publishing Switzerland 2014 vegetable. In fact, its chemical composition is almost similar to other commercial bast fibres, such as a-cellulose (60-70 %), hemicelluloses (15-20 %), lignin (5-10 %) and pectins (3-5 %) along with trace amount of water-soluble materials. The fibre exhibited high breaking tenacity (40-60 MPa) and high breaking elongation (3-5 %). In this chapter, okra bast fibre is introduced as a reinforcement material for fabrication of phenol formaldehyde resin composites. Manufacturing techniques and effect of fibre modification on their mechanical, thermal and biodegradation properties are discussed.

Keywords Okra bast fibre • Thermosetting phenol formaldehyde resin • Interface modification • Composite fabrication • Properties of composite

10.1 Introduction

Environmental awareness is encouraging scientific research to produce cheaper, environment-friendly and more sustainable packaging as well as construction mate­rials. Natural fibre-reinforced thermoplastic composites are strong, stiff, light weight and recyclable and have the potential to meet this requirement. Because of their low cost, low density and excellent mechanical properties, natural fibres such as sisal, jute, hemp, flax, banana, PALF, coir and palm are promising reinforcement with thermoplastic composites (Sreekumar et al. 2011; Kabir et al. 2012; Virk et al.

2012) . Among the 2,000 fibre-containing plants species, fewer have economical value. Jute and hemp were extensively used from past days (Mwaikambo and Ansell 1999; Mondal and Khan 2008). But high production cost with large cultivation area limits its use. Okra bast fibre (OBF) is a lignocellulosic fibre which is obtained from okra plant that grows everywhere abundantly in the world. Nowadays, it is rejected as agricultural waste products. However, due to the favourable mechanical properties of OBF, it has been transferred successfully to thermoplastic composite materials so far (Fig. 10.1).

OBF comes from the species ‘esculentus’, in the family ‘malvaceae’. It is culti­vated throughout the tropical and warm temperate regions of the world for its fibrous fruits or pods containing round, white seeds. The fruits are harvested when imma­ture and eaten as a vegetable. The vegetable can be collected from plant up to the period of 3-6 months. The plant was then subject for direct combustion. This opera­tion causes not only environmental pollution but also waste valuable fibre compo­nents. The chemical composition of OBF is a-cellulose (60-70 %), hemicelluloses (15-20 %), lignin (5-10 %) and pectins (3-5 %) along with trace amount of water — soluble materials (Khan et al. 2009). Though it contains higher percent of cellulose, it may have potentiality to make good-quality composite with thermoplastic/ thermoset resins. Fortunati et al. (2013) prepared OBF-PVA composites and stud­ied its degradation properties. The fibres possess good mechanical properties and biodegradable characteristics. But such properties are not sufficient as engineering or commodity plastics. Besides, like other vegetable fibres, OBF possesses few

weak points such as hydrophilic nature and degradation after prolong exposure to sunlight and is much prone to creasing, possibly due to high degree of orientation of cellulose in the fibre.

Thermoset resins are promising materials for natural fibre composite industries because they are insoluble and infusible and have high-density networks. A number of studies have been reported on thermoset-plastics-natural fibre composites. Injection and extrusion moulding processes for fabrication of short fibre/thermoplastic com­posites are proficient and economic (Sun et al. 2010; Paulo et al. 2007). In extrusion moulding process, fibres are well distributed into a matrix which is most desirable for enhanced composite properties. Besides, fibre content, fibre diameter, fibre length, void content, fibre orientation and fibre-matrix bonding are very important parameters for natural fibre-reinforced thermoplastic/thermoset-plastic composites (Joseph et al. 1993; Alam et al. 2010). Kalaprasad et al. (1996) found high mechani­cal strength, modulus and thermal resistance of sisal/glass hybrid fibre-reinforced low density polyethylene (LDPE) composites by varying fibre length and fibre distribution. Void possesses in composites reduced mechanical properties. Again, weak interface between fibre and matrix increases the probability of void content in composite as a result decreases the flexural strength, the off axis strength and the compression strength. Improvement of interfacial strength gives substantial improvement in tensile strength and modulus of short fibre composites. Since the chemical nature of fibre and matrices is different, strong interfacial adhesion is compulsorily required for an effective transfer of stress. Ray et al. (2001) reported that alkali-treated jute improves interfacial bonding of jute/vinylester composites.

Mild alkaline treatment creates rough surface topography of fibre by removing both intercellular and adhering impurities. On the other hand, fibrillation took place (breakdown the fibre bundle into smaller fibres) when fibre was treated in strong alkaline condition. As a result, the effective surface area of fibre increases which help it for easy wetting in matrix resin. Therefore, by increasing the fibre aspect ratio through alkali treatment, it can be possible to get better fibre-matrix interface adhesion and increase of mechanical properties (Weyenberg et al. 2006). This chapter deals with the fabrication process of OBF-PFR composites and their mechanical, thermal and biodegradation studies.